1. Field of the Invention
The present invention relates to a method for polishing a semiconductor wafer, especially to a method for polishing the semiconductor wafer by using a both-sides polishing apparatus to polish both side surfaces of the semiconductor wafer simultaneously.
2. Description of Prior Art
The flatness requirements for a semiconductor wafer are stricter than ever before. One of methods for the flatness of the semiconductor wafer is using a both-sides wafer polishing apparatus to polish both side surfaces of the semiconductor wafer simultaneously.
While polishing on the method, water layers containing grinding grains are sometimes formed between the wafer carrier and the polishing pads of the wafer polishing apparatus. This causes the semiconductor wafer to move freely between the water layers or even fall between the wafer carrier and the polishing pads. Furthermore, the friction between the wafer and the wafer carrier may damage the surfaces of the wafer.
The semiconductor wafer is not easily detached from the polishing pad under the water tension on the surfaces of the polishing pad. This may result in that the semiconductor wafer can not be retrieved.
Japanese Patent Laid Open 2-294032 and 2-36066 disclose methods to overcome the above problems, in which grid grooves are provided on the polishing pads to discharge the water on the polishing pads into the periphery of the polishing pads.
Accordingly, water layers are not formed on the surfaces of the polishing pads, and the water tension between the pad and the wafer can be reduced.
By using the polishing pads provided with grid grooves on the surfaces thereof, the semiconductor wafer can be easily detached from the polishing pad on the side of a lower polishing plate. However, the wafer adheres to the polishing pad on the side of an upper polishing plate when the upper polishing plate is lifted. As a result, the wafer can not be retrieved by the retrieving apparatus. Consequently, the wafer may fall and break.